Re: [PATCH] soundwire: bus: add enumerated slave to device list

From: Pierre-Louis Bossart
Date: Wed Sep 09 2020 - 13:01:36 EST

On 9/9/20 10:54 AM, Srinivas Kandagatla wrote:

On 09/09/2020 15:39, Pierre-Louis Bossart wrote:

Currently slave devices are only added either from device tree or acpi
entries. However lets say, there is wrong or no entry of a slave device
in DT that is enumerated, then there is no way for user to know all
the enumerated devices on the bus.

Sorry Srinivas, I don't understand your point.

The sysfs entries will include all devices that are described in platform firmware (be it DT or ACPI).

yes that is true, but it will not include all the enumerated devices on the bus!

In my case on a new board I was trying to figure out what devices are on the bus even before even adding any device tree entries!

We've seen this before but dynamic debug provides all the information you need. see e.g. the logs from

jf-cml-rvp-sdw-1 kernel: [  289.751974] soundwire sdw-master-0: Slave attached, programming device number
jf-cml-rvp-sdw-1 kernel: [  289.752121] soundwire sdw-master-0: SDW Slave Addr: 10025d070000 <<< HERE

Yes, I have noticed this too! This will be printed for every call to sdw_extract_slave_id()!


Now I get your point but
a) you already have a dynamic debug trace to list all devices
b) adding 'undeclared' devices would make things quite murky and is only half of the solution. We already struggle because we already have 'ghost' devices in sysfs that are not physically present, and no way to differentiate between the two. If we did add those entries, then we'd need two new sysfs attributes such as
'declared' and 'enumerated'.

I totally agree with you on dealing with the undeclared devices, which is unnecessary mess!

It's not necessarily that bad.
- if the intent is to have a single platform firmware that can deal with different boards, it's a good thing.
- but if it's just sloppy platform firmware that just does copy-paste from platform to platform then indeed it becomes a mess.

May be we could make the enumerated devices discovery bit more verbose!

Maybe adding a device number sysfs entry would help, e.g. reporting
NotAttched or a value in [0,11] would tell you if the device is actually present.